Estimation of movement

ABSTRACT

A mobile transceiver and a method of detecting movement of the mobile transceiver in a radio system. The radio system includes at least one base station and terminals. The movement of the mobile transceiver is measured by at least one acceleration sensor ( 114–116 ) to take the movement of the mobile transceiver onto account in the operation of the radio system.

FIELD OF THE INVENTION

The invention relates to a solution for detecting movement of a mobiletransceiver in a radio system.

BACKGROUND OF THE INVENTION

In radio systems, such as the GSM (Global System for MobileCommunication), CDMA (Code Division Multiple Access), WCDMA (Wide BandCDMA), CDMA 2000, PDC (Personal Digital Cellular) and the like, themovement of a mobile terminal is not usually measured in any way but theoperations of the whole radio system are designed so that the datatransmission connection works in all conditions. In that case operationsare performed as if the terminal moved all the time at a very high rateon the border of the coverage area of two or more base stations in acity during daytime. Consequently, the loading of base stations and theinterference level are high and channel changes as great as possible.This wastes resources and power, and increases the interference levelbecause several measuring and signalling operations are performed alltoo often with respect to what the real movement of the terminalrequires.

BRIEF DESCRIPTION OF THE INVENTION

The object of the invention is to improve estimation of movement andadjust the operations of a radio system to the movement. This isachieved with a method of detecting movement of a mobile transceiver ina radio system, which comprises at least one base station and terminals.The method further comprises measuring the movement of the mobiletransceiver by at least one acceleration sensor to take the movement ofthe mobile transceiver into account in the operation of the radiosystem.

The invention also relates to a mobile transceiver in a radio system,which comprises at least one base station and terminals. The mobiletransceiver is further arranged to measure its movement with at leastone acceleration sensor to take the movement of the mobile transceiverinto account in the operation of the radio system.

The method and system of the invention provide several advantages. Thepower consumption of the mobile transceiver can be reduced, the radionetwork capacity increased and the quality of data transmissionimproved.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in greater detail by means ofpreferred embodiments with reference to the accompanying drawings, inwhich

FIG. 1 is a block diagram illustrating a radio system,

FIG. 2 is a block diagram illustrating a transceiver,

FIG. 3 is a block diagram of an FIR filter

FIG. 4A illustrates accelerations caused by walking in the direction ofdifferent dimensions, and

FIG. 4B illustrates accelerations when one answers a call.

DETAILED DESCRIPTION OF THE INVENTION

The solution of the invention is applicable to a mobile transceiver of aradio system, in particular.

First the radio system will be described by means of FIG. 1. A typicaldigital radio system comprises a base station 1, mobile transceiverunits 2 to 4 and a base station controller 5. The base station 1communicates with mobile transceiver units 2 to 4 using signals 6 to 8.The base station 1 is connected to the base station controller 5 by adigital transmission link 9. The mobile transceiver units 2 to 4 areterminals, e.g. mobile stations. The signals 6 to 8 between the basestation 1 and the mobile transceivers 2 to 4 include digitisedinformation which is e.g. speech or data information produced bysubscribers or control information produced by the radio system.

FIG. 2 is a block diagram illustrating a mobile transceiver. Thetransceiver comprises an antenna 100 for transmission and reception.When a signal is received, it propagates from the antenna 100 to aduplex filter 102, which separates receiving circuits from transmittingcircuits. The duplex filter 102 passes the received signal to a radiofrequency block 104 of the receiving side, where the receivedradio-frequency signal is converted into the base band. From the radiofrequency block 104 the analogue baseband signal propagates to ananalogue-digital converter 106, which converts the analogue signal intoa digital one. From the AID converter 106 the digital signal furtherpropagates to a signal processing block 108, where the signal can befiltered, decoded and demodulated, for example. From the signalprocessing block 108 the signal often propagates to other blocks of thetransceiver, which are not relevant to the invention and are thereforenot shown here.

When a signal is transmitted, it arrives in the signal processing block108, where the signal to be transmitted can be filtered, encoded ormodulated, for example, and propagates further to a digital-analogueconverter 110, which converts the digital signal into an analogue one.The analogue signal is converted into a radio frequency signal in amixer included in the radio frequency block 112. The radio frequencysignal propagates to the duplex filter 102, which further guides theradio frequency signal to the antenna 100, which emits the signal intoits environment as electromagnetic radiation.

The signal processing block 108 measures the impulse response in amanner known per se, for instance. In the present solution themeasurement frequency of impulse response depends on the movement of thetransceiver. The movement is measured by at least one accelerationsensor 114 to 116. The acceleration sensor is usually an electromechanicconverter, which produces an electric signal corresponding to theacceleration at its output pole. The operation of the accelerationsensor is based e.g. on a piezoelectric crystal, where the change ofcharge distribution is comparable to the force directed at the crystal.Acceleration sensors are described in greater detail in UnderstandingSmart Sensors, Frank Randy, Artech House Inc., 1996 (ISBN0-89006-824-0), which is incorporated herein by reference.

The movement can be measured in more than one dimension by using severalacceleration sensors, which can be integrated into the same sensor. Byusing at least three acceleration sensors which are in the directions ofdifferent dimensions the terminal state can be measuredthree-dimensionally. The acceleration signal measured by theacceleration sensors 114 to 116 is fed into the digital signalprocessing block 108, where the measurement frequency of impulseresponse, for example, is controlled according to the accelerationinformation and/or the velocity calculated from the accelerationinformation. The higher the measured acceleration or the velocity is,the more frequently the impulse response is measured. The lower themeasured acceleration or the velocity, the less frequently the impulseresponse is measured.

In addition to the acceleration or instead of it, the terminal velocitycan be measured by integrating the acceleration. Mathematicallyexpressed, the velocity v is obtained as an integral of acceleration aas follows:

v = ∫_(t₀)^(t₁)adtwhere t₀ is the starting time of measurement and t₁ is the ending timeof measurement, i.e. the time interval t₁ to t₀ is the measuring timewindow. The velocity v measurement can be expressed in discrete form asfollows:

$v = {\sum\limits_{i = 1}^{M}{a_{i}\Delta\; t_{i}}}$where M is the number of measuring moments in the measuring time window,a_(i) is the acceleration at each measuring time and Δt_(i) is the timebetween two measuring moments. In the solution described the measurementfrequency of impulse response increases as the terminal velocityincreases. Correspondingly, the measurement frequency of impulseresponse decreases as the terminal velocity decreases.

Since the mobile transceiver does not move all the time at a very highvelocity on the boarder of the coverage area of highly loaded basestations, the power consumption of the mobile transceiver can be reducedconsiderably by decreasing the measurement frequency of impulseresponse. The power consumption can at most be reduced to less than1/3000 of the power consumption in a situation where the mobiletransceiver does not take its movement into account. In a subscriberterminal, the reduced power consumption means longer charging intervalsof the battery both in the standby mode and in the talk mode. When themovement of the mobile transceiver requires the highest possiblemeasurement frequency of impulse response, the measurement frequency canbe e.g. 100 Hz. On the other hand, when the transceiver is at leastnearly immobile, the impulse response can be measured at a frequency of1 Hz, for example. According to the example described, the impulseresponse measurement frequency can thus be reduced 100-fold. Themeasurement frequencies given only exemplify the operation and give anidea of the influence of the present solution on the measurementfrequency of impulse response. The solution described is limited neitherto the above-mentioned measurement frequencies nor to the ratios of themeasurement frequencies given. At its simplest the impulse response canbe measured at two frequencies. In that case a low measurement frequencyis used when the mobile transceiver is immobile or moves slowly (at thehuman walking pace, less than 10 km/h). Otherwise a high measurementfrequency is used. It is not the measurement frequencies that areimportant but the fact that the low impulse response measurementfrequency should be lower than the high impulse response measurementfrequency.

The information on the impulse response is used e.g. in the followingmanner. The base station or base stations with which the terminalcommunicates over a data transmission connection are searched for bymeans of the impulse response measurement. The search is carried out bymeasuring the impulse response from one or more base stations andselecting at least one base station with the highest signal interferenceratio SNR or the highest, signal noise ratio SNR. The impulse responsemeasurement is used for updating the list of neighbouring base stationsfor a possible handover. The impulse response measurement is alsoemployed for timing synchronization between the terminals and the basestations. In addition, the starting transmission power of the terminalis determined at the beginning of connection establishment by means ofthe impulse response measurement.

When the velocity of the mobile transceiver is measured by integratingacceleration, the velocity estimate formed can be used for controllingthe transmission power of the mobile transceiver. In that case the stepsize of power control, for example, can be optimised. The step size ofpower control is the smallest change in power that can be made. This isexplained in greater detail in T. Frantti, Fuzzy Power Control forMobile Radio Systems, European Symposium on Applications of IntelligentTechnologies, Aachen, Germany, 1997 and in A. J. Viterbi,CDMA—Principles of Spread Spectrum Communications, Addison Wesley, 1995,which are incorporated herein by reference. By means of velocity thethreshold for power control can also be changed so that as the velocityexceeds a predetermined velocity threshold, the power is controlleddifferently than when the velocity is below the predetermined limit. Oneor more such thresholds may be used. Instead of velocity thresholds, thepower control can also be changed slidingly, i.e. constantly accordingto the velocity. Furthermore, the velocity can be used for determiningthe measurement accuracy of impulse response, i.e. for optimizing thelength of the FIR filter (Finite Impulse Response).

The FIR filter will now be described in greater detail by means of FIG.3. The FIR filter comprises delay means 300, taps 302 and an adder 304.The taps 302 of the FIR filter are weighting coefficients of the impulseresponse. When the coefficients are correct, the distortion caused bythe channel decreases to its minimum. At their simplest the tapcoefficients are either ones or zeroes. An incoming signal x(t) isdelayed in each delay means 300 and the delayed signals are addedtogether in the adder 304. At its simplest the FIR filter is a transferregister where the content of each register element is added, weightedby a tap coefficient. In the time plane the output y(t) of the FIRfilter can be expressed by the formula

${y(t)} = {\sum\limits_{k = 0}^{M - 1}{{h(k)}{x\left( {t - {k\;\Delta\; t}} \right)}}}$where h(k) is the tap coefficient of impulse response, k is an indexfrom 0 M to 1, M is the number of taps, t is the time and x(t) is thesignal value at the moment t, y(t) is the signal estimate of thereceived signal.

When the channel distortion is not very great, accurate information onimpulse response is not needed. In that case it is not necessary tomeasure or define all M taps of the FIR filter but it is sufficient thatP taps, where P is smaller than M, i.e. P<M, are used for defining thesignal estimate. Undefined taps receive the value 0.

When the velocity of the mobile transceiver is measured, reliableinformation can also be formed from the influence of the Dopplerphenomenon on the frequency shift of the signal received. The frequencyshift Δf_(i) caused by the Doppler phenomenon to the component i of onesignal is expressed mathematically as follows:

${{\Delta\; f_{i}} = {\frac{v}{\lambda}\mspace{14mu}\cos\;\alpha_{i}}},$where i is the index of the signal component, λ is the signal wavelength, v is the transceiver velocity and α_(i) is the angle between thedirection of movement of the transceiver and the direction of thearriving signal. The frequency shift Δf of the received signal alsochanges the duration of the received symbol, which should be taken intoaccount in data transmission. In transmission the symbol duration can beeither increased or reduced according to the influence of the Dopplerphenomenon.

The received signal should be sampled (block 106 in FIG. 2) at theNyquist frequency in proportion to the greatest frequency shift Δfcaused by the Doppler phenomenon. In the solution shown the samplingfrequency can be changed according to the frequency shift Δf. Thesampling frequency is increased when the frequency shift increases andreduced when the frequency shift decreases.

When all K signal components are gone through, i being 1 to K (i=1, . .. , K), where K is the desired number of signal components, it ispossible to form the power density spectrum of Doppler spread. If weassume that different signal components have scattered isotropically andarrive at the receiver spread equally in all directions between [0°,360°], we obtain a U-shaped power density curve. The bandwidth f_(D) ofDoppler spread can be estimated from the power density spectrum ordirectly from the greatest frequency shift. The inverse of the bandwidthprovides delay spread T_(C), T_(C)=1/(2·f_(d)), where the band widthf_(D) is f_(D)=(v/c)·f_(C) and f_(C) is the frequency of the carrierwave. Coherence time, i.e. the time when channel changes are small andthe symbol transmitted on the channel contains hardly any channelinterference, can be determined from the delay spread or directly fromthe bandwidth of Doppler spread. Doppler spread isDoppler_spread=2·(v/c)·f_(C)=β_(d). The coherence time T_(C)=1/β_(d). Ifthe symbol duration is shorter than the coherence time, the channel is aslowly fading channel. If the symbol duration is longer than thecoherence time, the channel is a fast fading channel. When it isdetected that the coherence time T_(C) changes due to the Dopplerphenomenon, source coding, channel coding, power control or datatransmission rate can be changed in the solution shown so that theinfluence of the Doppler phenomenon is reduced or eliminated. The ratioof the coherence time to the symbol duration defines the channel as aslow fading or a fast fading channel.

Context identification related to each movement can also be carried outeven by one acceleration sensor, but preferably by several accelerationsensors. This is illustrated in FIGS. 4A and 4B, where the vertical axisrepresents the output voltage U corresponding to the sensor accelerationin volts V and the horizontal axis represents the sample number Ncorresponding to the time T. The same sampling frequency is used both inFIG. 4A and in FIG. 4B. By means of context identification it ispossible to distinguish immobility, walking, running and sitting in thecar, etc. from one another on the basis of the behaviour of accelerationsignals generated in the above-mentioned states. FIG. 4A shows theacceleration curves of three sensors, which measure in differentdirections, as a function of time when the user steps at the usualwalking rate, i.e. 50 samples on the horizontal axis correspond toapproximately one second. The sensors are attached to a terminal carriedby a user who walks. Walking and running generate regular detectableaccelerations in the up and down directions. Walking and running can bedistinguished from the other states and from each other on the basis ofthe amplitude and the frequency of the acceleration signal. When theuser is immobile, usually hardly any acceleration occurs or accelerationis caused e.g. by the fact that the user turns, turns his head, etc.which can be detected and distinguished from the actual movement withrespect to the ground surface. FIG. 4B shows a situation where the useranswers the phone used as the terminal. The phone is lifted to the ear,which causes typical acceleration curves in the direction of differentdimensions. In the case of a car, the terminal velocity can bedetermined e.g. from start, stop and curve accelerations. Contextidentification is described in greater detail in E. Tuulari, ContextAware Hand Held Devices, VTT Publications, 200, which is incorporatedherein by reference.

Acceleration sensors can be integrated into terminal circuits or frameand the acceleration information can be processed by the processor inthe terminal or by a separate processor in the signal processing block(FIG. 1, block 108).

Even though the invention was described above with reference to theexample according to the accompanying drawings, it is clear that theinvention is not limited thereto but may be modified in various wayswithin the inventive concept disclosed in the appended claims.

1. A method of detecting movement of a mobile transceiver in a radiosystem, which comprises at least one base station (1) and terminals(2–4), comprising the steps of: measuring the acceleration of the mobiletransceiver (2–4) by at least one acceleration sensor (114–116) anddetermining the velocity of the mobile transceiver by integrating theacceleration, and determining the frequency shift caused by the Dopplerphenomenon at the frequency used for data transmission from the velocityof the mobile transceiver (2–4), in order to take the movement of themobile transceiver into account in the operation of the radio system. 2.The method according to claim 1, further comprising the step ofmeasuring the acceleration of the mobile transceiver by at least oneacceleration sensor (114–116) and determining the velocity of the mobiletransceiver from the acceleration information by means of contextidentification.
 3. The method according to claim 1, by furthercomprising the step of changing the sampling frequency in receptionaccording to the magnitude of the frequency shift.
 4. The methodaccording to claim 1, further comprising the step of determining thecoherence time related to the Doppler phenomenon from the velocity ofthe mobile transceiver (2–4).
 5. The method according to claim 4,further comprising the step of changing at least one of the followingfactors that influence data transmission as the coherence time changes:source coding, channel coding and data transmission rate.
 6. The methodaccording to claim 1, further comprising the step of taking the velocityof the mobile transceiver (2–4) into account when the transmission powerof the mobile transceiver is adjusted.
 7. The method according to claim1, further comprising the step of determining the measurement frequencyof impulse response from the velocity of the mobile transceiver (2–4).8. The method according to claim 1, further comprising the step ofoptimizing the measuring accuracy of impulse response according to thevelocity of the mobile transceiver (2–4).
 9. The method according toclaim 1, further comprising the step of using at least threeacceleration sensors (114–116) to measure the movement of the mobiletransceiver (2–4) in three different spatial dimensions.
 10. The methodaccording to claim 1, further comprising the step of measuring themovement of the mobile transceiver (2–4) at least in two dimensions byat least two acceleration sensors (114–116).
 11. The method according toclaim 1, wherein the mobile transceiver (2–4) is a mobile station.
 12. Amobile transceiver in a radio system, which comprises at least one basestation and terminals, the mobile transceiver (2–4) being arranged andadapted to, measure the acceleration of the mobile transceiver (2–4)with at least one acceleration sensor (114–116) and determine thevelocity of the mobile transceiver (2–4) by integrating theacceleration, and determine the frequency shift caused by the Dopplerphenomenon at the frequency used for data transmission from the velocityof the mobile transceiver (2–4), in order to take the movement of themobile transceiver (2–4) into account in the operation of the radiosystem.
 13. The transceiver according to claim 12, wherein the mobiletransceiver (2–4) is arranged to measure the acceleration of the mobiletransceiver (2–4) with at least one acceleration sensor (114–116) anddetermine the velocity of the mobile transceiver (2–4) from theacceleration information by means of context identification.
 14. Thetransceiver according to claim 12, wherein the mobile transceiver (2–4)is arranged to change the sampling frequency in reception according tothe magnitude of the frequency shift.
 15. The transceiver according toclaim 14, wherein the mobile transceiver (2–4) comprises at least threeacceleration sensors (114–116) for measuring the movement of the mobiletransceiver (2–4) in three different spatial dimensions.
 16. Thetransceiver according to claim 14, wherein the mobile transceiver (2–4)is a mobile station.
 17. The transceiver according to claim 12, whereinthe mobile transceiver (2–4) is arranged to determine the coherence timerelated to the Doppler phenomenon from the velocity of the mobiletransceiver (2–4).
 18. The transceiver according to claim 17, whereinthe mobile transceiver (2–4) is arranged to change at least one of thefollowing factors that influence data transmission as the coherence timechanges: source coding, channel coding and data transmission rate. 19.The transceiver according to claim 12, wherein the mobile transceiver(2–4) is arranged to determine the measuring frequency of impulseresponse from the velocity of the mobile transceiver (2–4).
 20. Thetransceiver according to claim 12, wherein the mobile transceiver (2–4)is arranged to take the velocity of the mobile transceiver (2–4) intoaccount when the transmission power of the mobile transceiver (2–4) isadjusted.
 21. The transceiver according to claim 12, wherein the mobiletransceiver (2–4) is arranged to optimize the measurement accuracy ofimpulse response according to the velocity of the mobile transceiver(2–4).
 22. The transceiver according to claim 12, wherein the mobiletransceiver (2–4) is arranged to measure the movement of the mobiletransceiver (2–4) in at least two dimensions by at least twoacceleration sensors (114–116).